Shell pattern and method of casting therewith



A. SLATIS Sept. 24, 1946.

SHELL PATTERN AND METHOD OF CASTING THEREWITH Filed June 10, 1945 i Patented Sept. 24, 1946 UNITED STATES PATENT VOFFICE SHELL PATTERN AND METHOD OF CASTING THEREWITH Abraham Slatis, Chicago, Ill.

ApplicationJune 10, 1943, Serial No. 490,344

3 Claims. 1

This invention relates to the foundry art, and more particularly to improved processes for making articles of irregular shape, such as articles having undercut surfaces. Y

It is a principal object of the present invention to provide a feasible, economical method of making articles of irregular surface.

Another object is to provide a novel method whereby a large number of articles with underout surfaces may be made with the aid of a single set of dies.

Yet another object is to provide a method of casting large undercut objects, such as crank shafts.

A further object is to provide a practical method formaking a sand mold having pronounced undercuts therein.

Yet another object is to provide a novel foundry ,pattern capable of shaping an undercut mold and adapted to be removed from the mold so formed Without injury thereto.

Other objects and capabilities of the instant invention will rbe apparent from the description and claims which follow.

If an attempt is made to form a sand mold by means of a pattern of low melting alloy, and thereafter to remove the pattern by melting the same out of the mold, the bulk of gradually melting metal carries some of the sand with it so that the mold loses its shape. Again, if an attempt is made to melt a pattern of wax r other organic material out of a sand mold the melting wax or the like seeps into the sand, thereby deforming the mold. As this action continues the waxed sand falls out in chunks and ruins the mold.

The present invention utilizes metals, which because of their extremely high surface tension, do not seep into the sand. The disadvantages inherent in the use of massive metallic patterns are obviated by the use of extremely thin shells, reinforced against distortion by being tamped full of a readily removable reinforcing substance.

The gist of the present invention, therefore, resides in forming a metallic shell upon a die, from which the shell may be disengaged, reinforcing said shell with a removable backing, employing the reinforced shell to form a mold, and heating the interlocked mold, shell, and backing to bake the mold, separate the backing from the shell, and melt the shell out of the mold.

According to one embodiment of the present invention, a pair of complemental flexible molds are formed around a rigid pattern, said flexible molds are separated from said rigid pattern, an easily fused metallic shell is formed corresponding to the surface of the cavities in each of said molds, each of said metallic shells is. reinforced while supported in its flexible mold, by forming a backing therein removable by heating, the reinforced shells are extricated from the flexible dies in which they were formed, a set of refractory mold sectionsis formed with the aid of said reinforced shells, each assembly of refractory mold section, metallic shell, and `backing is heated above the melting point of the shell to bake said refractory mold sections and remove said shell and backing therefrom, said refractory mold sections are assembled into a complete mold, and said mold is employed to cast a replica of the pattern.

A feature of the present invention is the novel foundry pattern used therein, comprising a reinforced metallic shell capable of being readily .melted out of the mold which it is used to form, and with which it is interlocked. Such a foundry pattern may be fabricated, according to one exemplication of `my invention, by spray-coating a flexible mold with metal, tamping the shell thereby formed with sand or the like to reinforce the same, and disengaging the flexible mold from the reinforced metallic shell.

In order that my invention may be more fully understood, reference is had to the following eX- ample and to the accompanying drawing which illustrates the subject matter thereof in more or less schematic form, and indicates some of the principal advantages and capabilities inherent therein. In order to teach how to rpractice my invention, the following description is explicit, and more details than may be necessary are set forth therein and in the accompanying drawing, but it is distinctly to be understood that I do not limit myself to the exact steps, materials, proportions, and details of operation recited in the example or shown in the drawing.

The following example will be more readily understood by reference to the accompanying drawing, all the gures of which are more or less schematic longitudinal views in central vertical section.

Figure l shows the Vmetallic shell formed in the flexible mold.

Figure 2 shows a flask in process of preparation, wherein the flexible mold occupies the bottom of the flask, and the backing has been applied above the shell pattern.

Figure 3 shows the reinforced shell pattern disengaged from the flexible mold, with the flask inverted to a position preliminary to forming the refractory mold.

Figure 4 shows the refractory mold as formed and the flask arranged in position preparatory to baking the refractory mold and removing the shell pattern.

Like reference characters are used to designate similar parts in the drawing and in the following exempliiication of the invention.

Example A flexible mold :2 is formed corresponding to all or a portion of the article which it is desired to cast. This mold may be formed from a pattern (not shown) in the manner set forth in detail in my pending application S. N. 490,343, filed of even date herewith. Said exible half mold 2 conveniently is maintained in undistortedconfiguration by means of a sturdy rigid frame or annular ring I. Representative members of the class of substances of which the flexible half mold 2v may be made are soft vulcanized rubber and certain synthetic rubber-lik@ substances such as polymerized vinyl chloride compositions, molding compositions made from hydrated gelatin and glycerine, and the like.

The half mold 2 is sprayed with molten metal to form a shell 3 therein corresponding to the surface ofthe mold cavity. Ordinarily it is desirable to spray the undercuts with metal before spraying the rest of the flexible mold 2. Normally, the metal employed will have a relatively low melting point of the order of 300 to 400 F. inorder that the shell may readily be melted away-in the conventional equipment used for baking sand molds. The term metal as used in this specication and the appended claims refers to any pure metal, alloy, or mixture of metallic substances. Preferred representatives of this kclass are metals of relatively low melting point,

such as tin, type metal and babbitt. The spraying operation may be performed with conventional metal spraying apparatus.

Alternatively, the metal shell may be formed inthe mold by any desired technique of metal deposition, as for example by electroplatng. The use of a spray gun is preferred, however, because of the speed and simplicity of that'method. At the end of the metal coating operation, the assembly presents the appearance shown in Figure 1, with the thin metallic shell 3 in the half mold 2.

A second frame is keyed upon the frame I, as for example by means of guide pins 6, 6. This frame is tamped full of a reinforcing shell pattern backing substance 4 removable by heating the inverted assembly. Ordinary moist sand is the preferred member of the class of reinforcing substances, but other inert materials which will melt or crumble out of the mold upon heating may be employed. The assembled flask presents the appearance shown in Figure 2, the space above the shell 3 and half mold 2 being filled with the reinforcing substance 4.

A suitable mold board I (see Figure 3) may be fastened to the upper frame 5 so that when the flask is inverted the board 1 acts as a bot- Y tom board to support the shell reenforcing substance 4. The flask is then inverted and the exible half mold 2 is pried out of its supporting frame I and away from the shell pattern 3. The flask frame and contents thenpresents the apprearance illustrated in Figure 3. The working surface of the reinforced shell may be scrutinized, and if any` defects are discovered therein they may be corrected with carnauba wax or the like. The quantity of wax used for this purpose is so small that it has no undesirable effect upon the casting mold next to be formed.

A' conventional sectional mold may be substituted for the flexible half mold 2 to produce the shell pattern 3. If said sectional mold is made of metal, the sections thereof must be kept warm throughout the spraying operation; otherwise the sprayed metal 3 will peel away from the surface and said shell 3 will not conform precisely to the contours of the surface against which it was formed. After the shell 3 has been properly reinforcedY with a backing li, the sectional mold is freed from the shell pattern by being dismantled along lines of the undercut portion thereof.

In order to form the final casting mold (in two sections as postulated by the illustrative example), the reinforced shell may be forced into a suitable refractory substance, or the cavity above the shell pattern 3 ras shown in Figure 3 may be packed with a suitable material. Ordinary molding sand of the type used for making cores or dry molds is the preferred member of the class of refractories suitable for forming the final casting mold. Such sand ordinarily contains molasses or the like to improve its molding and baking properties. Other suitable refractories are slurries of plaster (such as plaster ofl Paris), cements and cementitious materials, such as magnesium oxychloride cements.

Usual means may be employed to form pouring gates and risers in the refractory Amold 8, in accordance with conventional practice. A second mold board 9 may be associated with the frameA I. The assembly is arranged in an oven in the manner illustrated in Figure 4. As there shown, the refractory mold 8 is placed upperlmost, the mold board 'l is removed and the ask is supported by contact of the frame 5 with the ledges I0, I0.

The assembly is baked at a temperature above the melting point of the shell 3, and preferably at the customary temperature for baking refractory molds such as sand molds. During this baking operation the reinforcing substance 4 will crumble as it dries and fall out of the flask. If desired, part of said material 4 may be mechanically removed from the flask prior to the baking operation.

The baking will also melt the shell 3. The molten metal runs out of the refractory mold section 8, and may be collected for salvage or use. Meanwhile, the refractory mold 8 is receiving Ya conventional baking. When theV baking operation is completed, the mold section contained in frame I is ready for use. Removal thereof from' the oven is facilitated by the mold board 9. The flask is inverted and the completed half mold 8 is inspected for flaws before being used inV a casting operation. In case any minor fault is discovered in the baked refractory mold section 8, the latter may be patched with molding sand to correct the same.

If the article to be cast is flat on one side, casting metal may be passed directly into the 05 cavity ofthe mold as it is supported on the mold board 9. Ordinarily, however, a plurality of refractory molds will be assembled into a mold, and the casting metal will be poured therein in accordance with usual foundry practice. Y'

Since both the cast article and its mold are rigid, and the two are interlocked by overlapping undercuts, the mold is broken to obtain the desired article. The molds may be handled in the usualV way common to dry sand molds.

From Vthe foregoing it is apparent that a new shell must be made for each refractory mold section. A large number of shells, however, can be made quickly and cheaply by repeatedly spraying or electroplating a single exible or sectional mold. 'I'hus it is necessary to make only one original pattern. From this pattern as many fiexible mold sections may be made as the scale of operations warrants; and a large number of shells may be formed successively in each exible mold section.

My improved process, utilizing my improved reinforced shells, is of utility in the manufacture by casting of even such large, convoluted, irregular, and undercut objects as crank shafts for marine engines and the like. It will be appreciated, however, that my new reinforced shells and the herein described process of using them,

may be advantageously employed to fabricate the widest variety of cast or molded objects, regardless of the size or shape thereof, or the material from which cast.

From the foregoing description it will be apparent that the instant invention has a wide range of industrial utility, and I claim all ramiiications and variations of my invention as set forth in the appended claims.

I claim:

l. The method of casting articles having undercuts therein, which comprises forming a pair of flexible half-molds around a rigid pattern, separating said exible half-molds from said rigid pattern, spray coating each of said flexible halfmolds with metal, reenforcing the metallic shells ing undercut surfaces which comprises forming thin low melting point shell patterns which together correspond to the shape of the article,

,forming a frangible mold section with each of said shell patterns, heating each aggregate comprising a shell pattern and mold section to bake the mold section and melt the shell pattern while supporting the same to permit the molten material comprising the shell pattern to flow from the mold cavity, and assembling the resulting baked mold sections to form a complete mold into which said -article with undercut surfaces may be cast.

3. The method of producing cast articles having undercut surfaces, which comprises forming a flexible sectional mold around a rigid pattern, forming thin shell patterns in the cavities of the sections of said iiexible mold, forming sand mold sections in contact with said shell pattern, and heating the assemblies comprising the shell patterns and sand molds to bake the sand molds and melt out the shell patterns.

ABRAHAM SLATIS. 

